POST support

[invernizzi]

Hey mechastorm,
thanks for the library. I've quickly added POST support, so that we can now create Toggl time entries with this library like so:

      print 'Creating time entry'
        response = toggl_client.query(
            '/time_entries/start',
            params={
                'time_entry': {
                    'description': 'hi',
                    'pid': project_id,
                    'tags': ['cli'],
                },
            },
            method='POST'
        )
        print 'Started!'